1. Field of the Invention
This invention relates to a catalyst for hydrotreating heavy hydrocarbon oils and more particularly to such a catalyst which is useful for removing sulfur compounds, nitrogen compounds and metallic compounds such as nickel and vanadium compounds, from the catalyst.
2. Description of the Prior Art
There is a recent world-wide tendency that petroleum products demanded are lighter fractions, resulting in raising problems as to the treatment of heavy hydrocarbon oils (heavy oils). Particularly, residual oils and the like which have been freed of useful lighter fractions, contain sulfur compounds, nitrogen compounds and metallic compounds in a very high concentration due to the concentration of these compounds therein. Methods for treating heavy oils to obtain lighter fractions therefrom include a method for hydrocracking and a method for fluid catalytic cracking. When the heavy oil is treated by the above method, the sulfur, nitrogen and metal compounds contained in the heavy oil are the cause for atmospheric contamination, degradation of performance of product oils or poisoning of catalysts.
Thus, it is increasingly important to hydrotreat heavy oils in order to remove therefrom the sulfur, nitrogen and metal compounds contained therein. The term "hydrotreat" used herein means to treat a feed catalytically under a hydrogen pressure in order to either convert the sulfur and nitrogen compounds in the feed to hydrogen sulfide, ammonia and the like for removal or cause the metal compounds to be deposited on the catalyst for removal. It is mainly light fractions and the like that have heretofore been subjected particularly to indirect desulfurization, and the feed so treated was that fraction which contained metal compounds in a small amount. Since, however, crude oils recently used worldwide as the feeds are heavier than the feed which has heretofore been used, such crude oils contain nickel, vanadium and other metal compounds in greater amounts, and processes for the direct desulfurization of residual oils have come to be very often carried out.
Problems raised at this point are as to the plugging of the pores of catalysts with metals and coke produced, whereby the catalytic activity is lowered and the operation of the apparatus hindered. Thus, in order to enable the apparatus to be operated in a stable manner, it is required that the metal compounds contained in heavy oils be effectively removed therefrom and catalysts having a long service life be developed.
In attempts to meet the above requirements, many proposals have been made. These proposals include a method for the prolongation of catalytic life which comprises using a catalyst carrier having pores of a uniform size or larger size in order to enable the metal-containing particles in the feed to diffuse as far as the interior of the catalyst so as to use the active sites located in the interior of the catalyst, a method comprising the use of a bimodal carrier having different distributions of pore size and a method comprising the selection of kinds of metals to be carried, the combination of the metals, and the adjustment of concentration of the metals.
These methods so proposed, however, do not necessarily solve the above problems.
The present invention was made in view of these problems.
The primary object of the present invention is to provide a catalyst for hydrotreating heavy oils, which will not be plugged in the pores with metals, coke and the like derived from the oils and will maintain the catalytic activity for a long period of time when used.